1. Technical Field
This invention relates to medical instruments and a method for use pertaining particularly to an improved intramedullary alignment guide and tool for accurately preparing and shaping the distal femur end surface to receive a knee prosthesis to be secured thereto.
2. Background Information
Knee surgery for the replacement and repair of knee joints has become commonplace in recent years. Total knee replacement systems and prostheses are available from a variety of manufacturers. Such total knee replacement systems, when properly installed, approximate the patient's natural knee movement. However, all knee prosthetic devices need to be properly fitted and installed to achieve an optimum fit and alignment. Proper alignment of the prosthetic device is critical to the successful outcome of a total knee replacement surgery. It is well known that it is desirable to provide an effective system of instruments and methods which ensure that the distal femur end is properly prepared for receiving the prosthetic device.
Some prior art systems have been developed which purport to assist a surgeon in preparing distal femur and proximal tibia ends for receiving knee prosthetic devices. One such system is shown in Petersen, U.S. Pat. No. 4,524,766. Petersen teaches a surgical knee alignment and cutting guide system which references a patient's mechanical axis, and from that reference, provides a cutting guide for shaping the patient's proximal tibia to receive the tibia portion of a knee prosthesis. Cutting guides are referenced from the tibia components of the knee prostheses for shaping the distal femur end to receive the femur portion of the knee prostheses. However, referencing from the patient's tibia introduces inaccuracies into the prosthetic alignment process. It is therefore desirable to provide an alignment system which references directly from the patient's distal femur end and provides for locating the patient's mechanical axis from the anatomic axis. By referencing from the patient's mechanical axis, an improved alignment system should employ an alignment guide and cutting guide to properly prepare the distal femur end for receiving the knee prosthetic device.
Another system for shaping the distal femur end is taught in Dunn, et al., U.S. Pat. No. 4,759,350. Dunn teaches a system of instruments for shaping the distal femur and proximal tibia surfaces to receive components of a knee prosthesis for knee replacement surgery. The Dunn system determines a patient's mechanical axis with reference to the patient's anatomic axis by using an alignment guide that is adapted to fit into a hole drilled into the distal femur end and intersecting the femoral intramedullary canal. Cutting guides or distal femoral resectors are attached to the alignment guide and are used to prepare the distal femur end to receive the femur portion of the prosthetic device.
The Dunn alignment guide is used to align the distal femoral resector or cutting guide so that a cut can be made in the distal femur end so as to provide a flattened bone end surface which is perpendicular to the patient's mechanical axis. The cut in the distal femur end is based upon a determination of the relative angular displacement of the patient's mechanical axis from the patient's anatomic axis. To enable a surgeon to cut the distal femur end properly and at the appropriate angle with respect to the mechanical axis, the distal femoral cutting guide is displaced relative to the intramedullary alignment guide such that a cutting slot in the cutting guide is exactly perpendicular to the patient's mechanical axis. The distal femoral cutting guide is secured to the alignment guide using a plurality of pins. A surgeon can pivot the cutting guide such that a cutting slot in the cutting guide is exactly perpendicular to the patient's mechanical axis. A pivot pin is fitted into the distal femoral cutting guide to allow the guide to pivot slightly with respect to the intramedullary alignment guide. The surgeon uses an alignment pin which may be inserted through one of a plurality of holes in the distal femoral cutting guide to achieve the desired angular displacement between the cutting guide and the alignment guide.
Disadvantageously, the system taught by Dunn requires that the distal femoral cutting guide pivot about the medial condyle of the femur when a surgeon inserts an alignment pin through one of the plurality of holes in the cutting guide and into the alignment guide. By pivoting about the medial condyle of the femur, and not about the intramedullary canal, the Dunn system increases the length of the cut across the distal femur end as the angular displacement between the distal femoral cutting guide and the alignment guide is increased. Conversely, as the angular displacement between the cutting guide and the alignment guide is decreased, due to a small angular displacement between the patient's anatomic and mechanical axes, the length of the cut in the distal femur end is correspondingly decreased. Therefore, there is a need for an improved intramedullary alignment guide which provides proper angulation of the prepared distal femur end yet allows the distal femoral resector or cutting guide to be pivoted about the patient's intramedullary canal.
To ensure that proper limb alignment is restored to a patient, a combination of intramedullary alignment devices and extramedullary alignment check rods have been used. The combination of intramedullary alignment devices and extramedullary alignment check rods increase the probability for a successful clinical outcome.
The prior art systems for preparing distal femur ends for receiving knee prosthetic devices are difficult to assemble, require an inventory having a number of small, easily lost components, and require significant operating-room time for their use. For example, the system taught by Dunn includes a femoral alignment guide, an anterior femoral cutting guide with locator, a distal femoral cutting guide, an AP measuring guide, a femoral finishing guide, and a system for preparing the proximal tibia end. A surgeon, after opening the damaged knee area, sequentially uses these instruments to prepare a patient's distal femur and proximal tibia ends to receive knee components of a selected prosthetic device. The various components taught by Dunn are difficult to assemble, and have a number of components which may be lost or misplaced during use and storage. For example, the Dunn system requires use of a pivot pin, an alignment pin, and a plurality of additional pins which are used to secure the distal femoral cutting guide in place after alignment. These pins have proven difficult to use as they are small and numerous, and hence easily misplaced.
Therefore, there is a need for an improved intramedullary alignment guide which facilitates quick and accurate alignment guide rotation, has no loose parts, no loose pins, is easily assembled, and which therefore reduces the amount of operating-room time necessary to use. The present invention provides such an improved intramedullary alignment guide.